Most transaction cards, such as bank cards issued by financial organizations or credit cards issued by credit companies, are provided with a diffraction grating or a hologram to prove the authenticity of those cards.
Expensive goods whose imitations often appear on the market, such as brand-name wrist watches, and cases or packaging for those goods are often provided with a diffraction grating or a hologram to prove the authenticity of the commodities.
A diffraction grating or a hologram (hereinafter referred to as “hologram or the like”) is applied to articles in various fields even outside the fields mentioned above because the hologram or the like is difficult to make or reproduce. The hologram or the like has become prevalent for its merits, such as its conspicuous interference colors, its excellent design, and the feature that the structure is destroyed if the hologram or the like is removed, making the transference of the hologram impossible.
Although the hologram or the like is difficult to reproduce, specialists in the field of hologram or the like know how to reproduce the hologram or the like. Since precision techniques are applied to counterfeit the hologram or the like, a counterfeit hologram or the like closely resembling an authentic hologram or the like can be formed. Therefore, it is very difficult to discriminate between a counterfeit hologram or the like and an authentic hologram or the like.
Various trials have been made to enhance the safety of the hologram or the like against counterfeiting.
An optical authenticity-proving image data recording medium recording CGHs (computer-generated holograms) representing first and second hologram patterns is disclosed in JP-A 2000-3124. The optical authenticity-proving image data recording medium projects transmitted diffracted light or reflected diffracted light forming a predetermined image proving the authenticity of goods when irradiated with monochromatic light. According to JP-A 2000-3124, a decision whether or not the goods are authentic can be easily made from the result of irradiation of the optical authenticity-proving image data recording medium with monochromatic light having a predetermined wavelength, i.e., whether or not the predetermined image is projected.
Since an area in which the hologram is formed by the prior art is large or the position of the area can be clearly known, the hologram can be easily detected and located, and the hologram can be easily analyzed. Thus, the safety of the prior art against counterfeiting is not sufficiently reliable.